The characteristics of radiation-induced mutagenesis and carcinogenesis will be investigated in the mouse embryo cell line, C2H 10T1/2. In order to determine the role of error prone repair in mutagenesis and carcinogenesis, we hope to isolate and study repair-deficient strains of this cell. Wild-type cells will be mutagenized with ethyl methanesulfonate, and repair deficient variants will be isolated after selection by a host-cell reactivation viral suicide technique. Repair-deficient strains will then be compared to the wild-type parental cells with regard to the frequency of mutation and transformation induced by UV and ionizing radiation delivered under varying conditions. Specific defects in DNA repair will then be characterized in each variant strain showing an altered frequency of induced mutagenesis and/or carcinogenesis, so that the role of various repair pathways in these processes can be delineated.